CONCEPTION DES DISPOSITIFS DE FRANCHISSEMENTS POUR LA FAUNE AMPHIDROME (CREVETTES ET POISSONS) DES COURS D'EAU ANTILLAIS : UNE REVUE.

Abstract

Stream macrobiota of the West Indies are dominated by amphidromous species of freshwater shrimps or prawns (Palaemonidae, Atyidae, and Xiphocarididae) and fishes (Gobiidae). If the growth and the reproduction of these species occur in fresh waters, their larval development needs salt water. Weirs and low-head dams for water abstraction may have impacts on both downstream and upstream migrations. Downstream migrations are performed out by newly hatched larvae which are swept by the water flow towards the sea. Water abstraction may induce a high entrainment mortality of larvae. Upstream migrations are carried out mainly by juveniles which present both higher positive rheotactic responses and higher climbing potentialities than adults. Juvenile individuals may have to get over the man-made barriers by climbing. Basic fishways were built on several occasions in the West Indies but no biotic criteria were really taken into account to facilitate the upstream migrations. Moreover the downstream migrations of the larvae were not taken into account. The necessity of maintening a free dam clearing in relation both to the life cycles and to the continuous reproduction of the species is recalled here. The entrainment mortality of larvae can be largely reduced if water is not abstracted during downstream migration which occurs mainly during the first hours after dusk. If water is abstracted continuously, light beams can be used to direct the larvae towards the compensation flows rather than towards the gauged flows. The imperviousnesses of low-head dams to upstream migrants can be eliminated by basic passage facilities such as « cascade-like passes » or « cross-side passes ».